Proteins which are the main component in meats are high molecular compounds of .alpha.-amino acids which are bonded by peptide bonds, and the molecular weight thereof is said, in general, to be 5,000 or more. It is apparent from experience that most of the components of "umami" (flavour enhancer) are in proteinous foods.
However, peptides in the state of a high molecular form are, though being rich in the native aroma of natural proteins, poor in the umami for instance, as anyone would so feel when he ate "sashimi" (slices of raw fish) of freshly caughed raw fishes or "beef mizutaki" (beef boiled plain), because the peptides in the said state could not release the components of umami therefrom.
Under the circumstances, a method of decomposing proteins for the purpose of flavour-enchancement of the components of umami has heretofore been proposed, and hydrolysis of proteins with an acid or alkali and decomposition thereof with an enzyme have been tried therefor. The former method of hydrolysis has an extremely limited utilizable range as the concentration of the salts formed is extremely high, and the detail thereof is not described herein. The latter method of decomposition with enzymes, to which the present invention belongs, is described hereinafter.
Various kinds of enzymes exist in tissues and digestive organs of animal meats, and these act for autolytic decomposition of proteins and fats. However, these include proteases, proteinases, peptidases, etc. as protein-decomposing enzymes, in mixture, and most of them individually have a high substrate specificity and the concentration of each enzyme and the reaction speed thereof are not uniform but are poor in the regularity. Accordingly, the molecular weight distribution of the decomposed solution is broad, randomly including high molecular peptides and components of an amino acid level, and this does not have any specific peak. This is proved by the molecular weight presumption by gel-chromatography of the decomposed solution with Sephadex G-50, whereupon an eluted curve is obtained, broadly extending in the total range of from a molecular weight of 1,500 to that of 30,000 which is the fractionation range of peptides and spherical proteins with the Sephadex G-50.
After the proteins are decomposed to the level of amino acids, the decomposed proteins may have the umami whilst not only these will lose the native aroma, taste and flavour of natural proteins but also these will have so-called strong amino acid odor or other offensive odor or will become highly bitter or rough.
Under the situation, the present inventors already proposed a means of overcoming the defect of the decomposition of proteins by autolysis only in Japanese Patent Publication No. 30344/55, where proteins are first completely autolyzed and decomposed and then the autolyzing enzymes are deactivated and desired amino acids are added so that the bitterness, roughness are some offensive odors are eliminated.
Further, the present inventors tried the following presumption in consideration of the above-mentioned known facts.
In the stage of high molecular weight peptides which is the initial stage of the protein decomposition, the aroma of raw material meats can be sustained but the umami cannot be derived from the meats, whilst in the level of amino acids which is the terminal stage of the protein decomposition, the umami can be derived but not only the native aroma of meats is lost but also the decomposed meats are to have some special bitterness, roughness and some other offensive odor which would deteriorate the umami.
Accordingly, it is presumed that the highest deliciousness capable of sustaining the native aroma of raw material meats while keeping the umami thereof would be obtained in the intermediate state of the said two stages, or that is, in the intermediate between the level of high molecular weight peptides and that of amino acids, which comprises peptide-bonded substances having a low molecular weight falling within a range of from 200 to 3000, especially in the concentrated formation of the said substances.
For the condition to realize the said presumption, the present inventors planned to add some other protein-decomposing enzymes besides the autolyzing enzymes, and as a first step, tried to make an experiment where the autolyzing enzymes are deactivated by heating or the like, after the completion of the autolysis therewith, and then other protein-decomposing enzymes are added anew.
As a result of the said experiment, it was found that in the above-mentioned addition method, the raw material meats are coagulated and dehydrated by the heating whereby the effective surface area of the meats to the enzyme reaction would decrease to result in the reduction of the enzyme reaction efficiency and the reduction of the yield thereof, while the molecular weight distribution of the products would often be uneven and most of the products would be bitter, and therefore, the resulting products would be unsuitable for umami seasonings or materials of foods.
In the above-mentioned case, even though exo-type protein-decomposing enzymes (belonging to a type capable of cutting a protein from the end chain thereof to decompose it into the constitutional amino acids), which may form a relatively small bitterness, were used, the formation of low molecular pepetides wall small but the meats were decomposed into the constitutional amino acids and other long chain and high molecular weight proteins.
Next, the present inventors tried to add other enzymes in the active stage of the autolyzing enzymes, expecting the synergestic composite reaction of the both enzymes. In the trial, three methods were repeatedly tested where the time of the addition of the enzymes was varied to be the initial, intermediate or terminal stage of the decomposition reaction, and as a result of the trial tests, the present invention has been achieved.
One object of the present invention is to achieve a method for preparation of tastable matters consisting mainly of low molecular weight peptides which have both the aroma and the umami.
Another object of the present invention is to provide tastable matters which can be utilized as extremely excellent food additives or seasonings.